Presentation by PD Dr. Michael S. Krzemnicki
In historic Eastern cultures (e.g. Mughal Empire), gems were often drilled or half-drilled to fix them with metal wires as a pendant on jewellery.
Later, some of these gems have been recut and re-used in new designs and styles.
Historic multi-gem necklace recently investigated at SSEF.
All gems are suspended (double half-drill) and mostly faceted but with strong wear marks!
Some of the faceted gems show half-drilled holes very close (and fragile) near the surface. It is assumed that these stones were reshaped and faceted at a later (but historic) age than the original drilling.
Relics of large drill-hole in a Sri Lankan sapphire. We assume that this stone was actually re-used and faceted from an even older jewellery (fixed through drillholes) when set into this brooch in the 1860ies.
Relics (drill-holes) from former setting.
What looks like a classic 19th century brooch with old cut diamonds…
…turns out to be green flint glass. The green colour is from traces of chromium.
Intriguingly, the green glass contains many eye-visible “spiky” inclusions, thus well mimicking a Colombian emerald.
Bracelet with pink sapphires painted orange on backside and in closed-back setting. To intensify colour and slightly shift it to ‘ruby’.
…dense mottled intergrowth of zoisite (complex Ca-Al-silicate) and plagioclase. Thus not jade!
Zoisite, first discovered in 1794 at Saualpe in Austria, it was soon after named after Sigmund Zois Freiherr von Edelstein (sic!) (1747-1819), nobleman and natural scientist.
Plagioclase, solid-solution (Na to Ca-Al-silicates) wihin the feldspar group. Its name comes from ancient Greek πλάγιος (plágios) 'oblique', and κλάσις (klásis) 'fracture’, in reference to its two cleavage angles. (afterWikipedia)
ct
Cr-photoluminescence emission
Absorption spectrum, purple colour mainly due to Feabsorption.
Forsterite (Mg2SiO4) inclusion in spinel
Photos and clip © A. Henn, except initial and final stages (by SSEF)
Cobalt spinel of 1.0 ct with a deep but vivid cobalt blue colour as a result of very high cobalt concentration (about 2100 ppm Co).
Cobalt spinel often contains about 40-200 ppm of cobalt. At this level, cobalt cannot be detected with chemical EDXRF analyses.
Recently we analysed a Cospinel with very high cobalt concentration (about 2100 ppm). Consequently, the cobalt is even visible in the EDXRF spectrum as a distinct shoulder besides the Fe-Kb peak.
SSEF GemTrackTM for a diamond
Based on microscopic observations and numerous spectroscopic criteria it was possible to confirm that the faceted pear-shaped diamond of 1.06 ct is the same as the rough diamond of 4.93 ct analysed by SSEF before cutting.
Synthetic moissanite of 1.8 ct with engraved girdle.
Characteristic doubling effect makes identification easy!
by Anna Hu
Interestingly, this ‘pearl’ pendant proved to be an assembled item made of two shell blisters.
Exceptional coral strand with 67 coral beads (up to 26.75 mm) of perfectly matching colour and quality. Their subtle but attractive pink colour is poetically also referred to as ‘angelskincolour’ (boke). Such corals are commonly attributed to Pleurocoralliumelatius .
DNA testing on three randomly selected coral beads of this necklace revealed, that they belong to a scientifically so-far undescribed
Pleurocoralliumspecies .
Recently, we have seen occasionally pink sapphires from Montepuez, Mozambique.
Three Greenland rubies of 2.39, 3.04 and 1.22 ct. Age dating was successful on a tiny zircon inclusion on the ruby of 1.22 ct (right).
Trace element signature of the investigated Greenland rubies is different to other rubies from ultramafic rocks.
Aappaluttoq ruby deposit in WGreenland.
Map: Krebs et al. 2019; Photo: Greenland Ruby A/S.
All three Greenland rubies were heated at high temperature and with significant glassy residues in healed fissures and cavities!
We calculated an age of 2.7 billion years for the zircon inclusion! This is well in accordance with literature describing the rubies from Greenland as the oldest ones known on Earth (e.g. Krebs et al. 2019)
Zircon (60 x 15 µm) before ablation after ablation
“Thepracticeistherefore,to roastthereddish[stones]so that the mixed colours are madetodisappear…Aruby stonehavingbeenroastedisreexamined, and,incaseitdoes notgainclarity,itisre-heated.
Al-Biruni (AD 973–1048)
• In most cases, heat treatment results in a change/shift of colour.
• The lower the heating temperature the more challenging is its detection! approx.temperaturerangesasbygemmologicalliterature
Heat treatment at low temperatures (about 700 – 1200 °C) is mostly applied to remove bluish zones and slightly shift purplish sapphires to a pink colour. before after 2h heating (oxidizing) at 1000 °C
Detection of any heat treatment is commonly relied on a combination of ‘classic’ microscopy, UV reaction, and spectroscopic analyses (Infrared- and Raman spectroscopy).
Very useful approach:
Phase transformations of hydroxides
Diaspore (α-AlOOH) and Goethite (α-FeOOH)
2 diaspore 1 corundum + water about 500 °C
2 AlOOH Al2O3 + H2O
2 FeOOH Fe2O3 + H2O 2 goethite 1 hematite + water about 350 °C
These are so-called dehydration reactions which occur when heating up these hydroxides (diaspore, goethite).
dotted vertical lines: main diaspore peaks
Sample 120993_6
Diaspore in Burmese ruby (Mogok)
Phase transformation
Diaspore in ruby (image width 2mm). before after dehydration
dotted vertical lines: main goethite peaks
Sample 85933_C3
Goethite in Mozambique ruby
Phase transformation
Goethite in fissure in ruby
from Sotheby’s International
Estrela de Fura 55.22 ct
Diaspore detected in fluid inclusion !
Sold at Sotheby’s auction in June 2023 for record $34.8 million.
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